With reference to FIG. 1, WO 2010/072710 discloses a power plant having a gas turbine unit 1 that comprises a compressor 2, a combustion chamber 3 and a turbine 4.
A mixture 6 comprising fresh air 7 coming from the environment is fed into the compressor 2 and flue gases 8 (deriving from the combustion of the mixture 6 with a fuel within the combustion chamber 3) emerge from the turbine 4.
The flue gases 8, which typically have a high temperature, are fed into a boiler 9 of a steam turbine unit 10; within the boiler 9 the flue gases 8 transfer heat to the water of the steam unit 10.
From the boiler 9, the flue gases 8 are split into a recirculated flow 12, that is cooled in a cooler 18 and mixed to the fresh air 7 to form the mixture 6 that is fed into the compressor 2, and a discharged flow 13, that is cooled in a cooler 19 and is then fed into a CO2 capture unit 14 to be then discharged into the atmosphere via 15; in contrast the CO2 that is captured in the CO2 capture unit 14 is stored in 16.
Different types of methods of CO2 capture are known; in the following some of them are briefly cited.
First method types include separation with solvents or sorbents. Among these methods, the method using amine (solvent) is the oldest; is was developed for gas stream having different conditions and features from those of a power plant; in particular this method was developed in connection with the oil industry in which typically a chemically reducing gas stream is treated; in contrast flue gases from a gas turbine have typically oxidising properties. Methods involving sorbents require the gas stream to flow through the adsorbent material at high pressure; regeneration occurs by lowering the pressure (Pressure Swing Adsorption) or increasing the temperature (Temperature Swing Adsorption).
Second method types include gas separation with membranes; different kind of membranes can be used, such as for example porous membranes, zeolites, polymeric membranes, and so on.
Third method types include cryogenic separation, involving gas stream cooling and condensation.
Therefore it is clear that a number of different possibilities are available to implement the CO2 capture method.